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Hawaiian Islands Synoptic Discussion and Guidance

807
FXHW60 PHFO 241422
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST SUN MAY 24 2015

.SYNOPSIS...COOL AND RELATIVELY DRY NORTHEASTERLY WINDS WILL
CONTINUE ACROSS THE ISLAND CHAIN THROUGH MONDAY. THESE WINDS WILL
CARRY LOW CLOUDS AND ISOLATED LIGHT SHOWERS MAINLY TO NORTHEAST
FACING SLOPES OF THE ISLANDS. LIGHTER WINDS ARE EXPECTED OVER MOST
OF THE STATE STARTING TUESDAY. AS A RESULT...A WEATHER PATTERN OF
NIGHTTIME LAND BREEZES AND AFTERNOON SEA BREEZES WILL RETURN TO THE
ISLANDS. THE SEA BREEZES WILL CAUSE CLOUDS AND ISOLATED SHOWERS TO
DEVELOP MAINLY OVER LEEWARD AND INTERIOR SECTIONS EACH AFTERNOON
DURING THE NEW WORK WEEK...WITH MOSTLY CLEAR SKIES EACH NIGHT.

&&

.DISCUSSION...
A RARE LATE MAY FRONT APPEARS TO HAVE STALLED JUST SOUTH OF THE BIG
ISLAND EARLY THIS MORNING. ELSEWHERE...THE CIRCULATION AROUND A 1011
MB SURFACE LOW NEAR 32N 151W...OR ABOUT 820 MILES NORTH NORTHEAST OF
HONOLULU...IS BRINGING COOL AND DRY NORTHEASTERLY WINDS INTO THE
ISLANDS NORTH OF THIS FRONT. AS A RESULT...THE ISLANDS CONTINUE TO
EXPERIENCE A VERY ATYPICAL LATE MAY WEATHER PATTERN.

ALOFT...A NORTHEAST TO SOUTHWEST ORIENTED UPPER LEVEL TROUGH IS
EVIDENT JUST EAST OF THE BIG ISLAND. AN UPPER LEVEL ANTICYCLONE IS
CENTERED ABOUT 880 MILES WEST OF LIHUE. THE GENERAL FLOW HIGH ABOVE
THE ISLANDS IS FROM THE NORTHWEST.

SATELLITE IMAGERY AND RADAR REFLECTIVITY DATA SHOW LOW CLOUDS AND
SHOWERS LINGERING SOUTHEAST OF THE BIG ISLAND. IT APPEARS THAT THE
MOST SIGNIFICANT RAINFALL HAS PUSHED SOUTH OF THE BIG ISLAND AT THIS
TIME. ADDITIONAL WIDESPREAD LOW CLOUDS REMAIN NEAR THE WINDWARD BIG
ISLAND. ELSEWHERE...BROKEN STRATOCUMULUS CLOUDS ARE BEING CARRIED
DOWN TOWARD THE SMALLER ISLANDS. THERE MAY BE SOME SHOWERS EMBEDDED
WITHIN THESE LOW CLOUDS...BUT THE CLOUDS MAINLY STABLE...SO THE
CLOUDS ARE LIKELY VERY LIGHT PRECIPITATION PRODUCERS. ANY SHOWERS
THAT DO ARRIVE IN THE ISLANDS AS THESE CLOUDS PUSH ONSHORE WILL
LIKELY AFFECT WINDWARD AND NORTH FACING SLOPES. MOST LEEWARD AREAS
ARE EXPECTED TO BE MOSTLY CLEAR AND DRY.

THE COOL AND RELATIVELY DRY NORTHEASTERLY FLOW HAS ALSO LOWERED DEW
POINTS FROM KAUAI TO MAUI. THE LATEST OBSERVATIONS SHOW DEW POINTS
ARE IN THE UPPER 50/S TO LOW 60/S ACROSS MOST OF THE SMALLER
ISLANDS...WHICH INDICATES THE ATMOSPHERE IS UNUSUALLY DRY FOR LATE
MAY. EXPECT SOMEWHAT COOL CONDITIONS BY DAY BREAK THIS MORNING AND
MONDAY MORNING...WITH OVERNIGHT LOW TEMPERATURES EXPECTED TO BE
AROUND 3 TO 5 DEGREES FAHRENHEIT BELOW NORMAL.

THE MODERATE NORTHEASTERLY LOW-LEVEL FLOW WILL CONTINUE THROUGH
MONDAY. AS A RESULT...RAINFALL WILL REMAIN MODEST AND CONFINED
PRIMARILY TO NORTHEAST FACING SLOPES...IN ADDITION TO THE UPSLOPE
SECTIONS OF KONA EACH AFTERNOON.

THE FORECAST MODELS CONTINUE TO SUGGEST THAT THE UPPER LEVEL TROUGH
THAT IS EAST OF THE ISLAND CHAIN MAY SHIFT WESTWARD TOWARD THE STATE
TUESDAY OR WEDNESDAY. THIS SHOULD WEAKEN THE PRESSURE GRADIENT
ACROSS THE AREA. THEREFORE...THE CURRENT FORECAST INDICATES A LIGHT
TRADE WIND PATTERN WILL DEVELOP STARTING TUESDAY. A WEAK SURFACE
TROUGH MAY ALSO DEVELOP IN THE VICINITY OF THE ISLANDS. IN THAT
CASE...A DIURNAL CONVECTIVE NIGHTTIME LAND BREEZE AND AFTERNOON SEA
BREEZE PATTERN WOULD LIKELY DEVELOP OVER MOST OF THE STATE. IN THIS
PATTERN...CLOUDS AND SHOWERS WOULD LIKELY DEVELOP MAINLY OVER
LEEWARD AND INTERIOR SECTIONS OF THE ISLANDS EACH AFTERNOON...
FOLLOWED BY CLEARING SKIES AT NIGHT.

&&

.AVIATION...
HIGH PRESSURE NW OF THE STATE WILL KEEP A N TO NE TRADE WIND FLOW IN
PLACE THROUGH THROUGH TONIGHT...WITH CLOUDS AND SHOWERS FOCUSED
PRIMARILY ACROSS N THRU E SECTIONS OF THE ISLANDS. CAN/T RULE OUT
SOME BRIEF MVFR CIGS AT PHTO...BUT GENERALLY VFR CONDITIONS ARE
EXPECTED AT ALL TERMINALS THROUGH 25/12Z.

NO AIRMETS ARE CURRENTLY IN EFFECT...BUT CAN/T RULE OUT A NEED FOR
AN AIRMET DUE TO MOUNTAIN OBSCURATION ACROSS N AND E SECTIONS OF THE
BIG ISLAND THROUGH MID MORNING. WILL CLOSELY MONITOR CONDITIONS AND
ISSUE AN AIRMET IF NECESSARY.

&&

.MARINE...
MODERATE TO FRESH NORTHEASTERLY WINDS WILL PERSIST TODAY. THE LATEST
SCATTEROMETER PASS FROM LAST EVENING INDICATED AN AREA OF 25 KT
WINDS JUST WEST OF KOHALA ON THE BIG ISLAND. THE LOCAL HIGH
RESOLUTION MODELS ALSO SHOW THE WINDS WILL REMAIN STRONG IN THIS
AREA THROUGH THIS AFTERNOON. AS A RESULT...A SMALL CRAFT ADVISORY
/SCA/ HAS BEEN POSTED FOR THE ALENUIHAHA CHANNEL AND THE NORTHERN
BIG ISLAND LEEWARD WATERS. THE LATEST FORECAST KEEPS WINDS BELOW SCA
CONDITIONS OVER ALL HAWAIIAN WATERS FROM TONIGHT THROUGH THE MIDDLE
OF NEXT WEEK.

AN EXTENDED PERIOD OF SOUTH SWELLS...WHICH HAVE BEEN GENERATED BY
THE FETCH ASSOCIATED WITH MULTIPLE SURFACE LOWS IN THE SOUTHERN
HEMISPHERE DURING THIS PAST WEEK...WILL MAINTAIN SOMEWHAT ELEVATED
SURF ALONG SOUTH FACING SHORES OF ALL ISLANDS THROUGH THE NEW WEEK.
OVERLAPPING SOUTH SWELLS ARE EXPECTED TO CAUSE SURF HEIGHTS TO
GRADUALLY APPROACH THE HIGH SURF ADVISORY CRITERIA ALONG MOST SOUTH
FACING SHORES DURING THE NEXT FEW DAYS. BASED ON THE CURRENT
FORECAST...SURF MAY REACH THE HIGH SURF ADVISORY THRESHOLD ALONG
MOST SOUTH FACING SHORES TUESDAY AND TUESDAY NIGHT. SURF HEIGHTS ARE
EXPECTED TO SUBSIDE SOMEWHAT ALONG SOUTH FACING SHORES AROUND
MID-WEEK.

ELSEWHERE...SMALL SWELLS FROM THE NORTH NORTHWEST AND WEST NORTHWEST
ARE EXPECTED TO MAINTAIN A LATE SEASON BUMP IN SURF HEIGHTS ALONG
MOST NORTH AND WEST FACING SHORES OF THE STATE EARLY THIS WEEK.
ALSO...A SMALL SHORT-PERIOD NORTH NORTHEAST SWELL ARRIVING TODAY IS
EXPECTED TO BOOST SURF HEIGHTS SLIGHTLY ALONG EXPOSED NORTH AND EAST
FACING SHORES OF THE ISLAND CHAIN THROUGH MONDAY. SURF HEIGHTS ARE
FORECAST TO REMAIN WELL BELOW THE HIGH SURF ADVISORY CRITERIA ALONG
NORTH...WEST AND EAST FACING SHORES THROUGH MID-WEEK. SEE THE LATEST
OAHU SURF DISCUSSION /SRDHFO/ FOR MORE DETAILS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 PM HST THIS EVENING FOR THE ALENUIHAHA
CHANNEL AND THE BIG ISLAND LEEWARD WATERS.

&&

$$

DISCUSSION/MARINE...HOUSTON
AVIATION...JELSEMA




Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office